In recent years it has been determined that various cardiac rhythm anomalies can be effectively treated by applying electrical stimulation pulses to the left side of the heart. In order to provide stimulation pulses to the left side of the heart, it is generally necessary to position an electrode accordingly. Initial efforts to place such an electrode involved highly invasive and traumatic surgery. This surgery required that the chest wall be opened and that an epicardial electrode be sewn or otherwise attached to the heart.
More recently intravascular leads have been developed. The electrode of these leads can be brought into contact with the left side of the heart by advancing the lead through the vena cava, right atrium and coronary sinus into the great vein of the heart. Once there, the electrode can be further advanced toward the apex of the left ventricle through one of the veins that descend from the great vein. See, for example, U.S. Pat. Nos. 5,803,928,; 5,755,766; and 5,755,765 and assigned to Cardiac Pacemakers, Inc.
Leads of the type described in the aforementioned '928, '766 and '765 patents offer significant advantages. Such leads provide a suitable electrical path for delivery of pulses from the cardiac rhythm management device to the left side of the heart. Such leads are also capable of sensing electrical signals otherwise associated with the left side of the heart and transferring these signals back to the cardiac rhythm management device. More importantly, these leads can be placed without the patient receiving the trauma associated with placing a patch electrode on the exterior of the heart.
The efficacy of leads described in the '928, '766 and '765 patents can be enhanced by providing means for ensuring that the electrode associated with the distal end of the lead remains in contact with the vessel wall. Providing a suitable means for ensuring such consistent contact is not easily achieved. The path the lead follows is circuitous and narrow requiring that the lead be very small in diameter and very flexible. Use of a traditional lead fixation device diminishes the flexibility of the lead and increases its diameter. Also, traditional lead fixation devices include tines or other projections which could interfere with advancement of the lead through the vasculature or even damage the vessel wall. Further, sometimes it is necessary to explant a lead for various medical reasons. Thus, the fixation device should be designed to permit the lead to be extracted.